1. Field of the Invention
The present invention relates to a tip assembly of a ball point pen, and more particularly to a tip assembly of a ball point pen, wherein the tip assembly comprises a writing ball, a ball housing a front end portion of which rotatably holds the writing ball therein, and a holder on a front end portion of which the ball housing is fixedly mounted.
2. Description of the Related Art
In writing operations, a writing ball rotatably mounted in a front end portion of a ball point pen is brought into contact with a recording medium such as a sheet of paper and the like (herein after referred to simply as the paper) which gives a frictional resistance to the writing ball to cause the ball to rotate. Such rotating ball draws the ink out of an ink reservoir of the ball point pen to apply the thus drawn ink to the paper. In a conventional ball point pen, as shown in FIGS. 3 and 4, the writing ball 21 is formed from a thin wire member, and rotatably held in a bore drilled in a front end portion of the ball housing 22 by caulking a peripheral portion of the bore. Prior to performing such caulking operation of the bore in the front end portion of the ball housing 22, an ink channel member 4 provided with a plurality of radial grooves 3 for forming ink flow passages is mounted in the bore. Consequently, after completion of the caulking operation, the writing ball 21 is seated on a seat surface of the ink channel member 4.
Until recently, in most cases, the ink used in the ball point pen has been of oil-based solution type. However, in these day, ink of aqueous solution type tends to be increasingly used in the ball point pen. The aqueous solution type ink comprises: aqueous liquid type ink; and, aqueous gel type ink. The latter, i.e., aqueous gel type ink is larger in viscosity than the aqueous liquid type ink, and capable of keeping its viscosity at relatively high level when stored. However, in writing operations, the aqueous gel type ink has its viscosity decreased since the aqueous gel type ink has a so-called "thixotropy properties". Due to the presence of such thixotropy properties, even when the aqueous gel type ink is used in the ball point pen, there is a fear that the ink leaks from the tip portion of the ball point pen to damage a user's clothes and documents, particularly pockets of the user's clothes. In order to solve the above problem, the conventional ball point pen is provided with a mechanism (shown in FIG. 4) for prevent the ink from leaking the tip portion of the ball point pen. In this conventional mechanism shown in FIG. 4, a compression coil spring 24 is inserted between the writing ball 21 and an inner axial front surface of the holder 23 so as to extend over substantially the entire length of the ball housing 22, and thereby resiliently urging the writing ball 21 forward.
However, in this conventional mechanism, as shown in FIG. 4, the coil spring 24 is constructed of three portions, i.e.,: a rear seating portion 24a; an intermediate portion 24b which is smaller in outer diameter than the rear seating portion 24a; and, a front linear portion 24c which is further smaller in outer diameter than the intermediate portion 24b. Since the coil spring 24 is very small in size and should be precisely formed in production, it is hard to produce such tiny and complicated coil spring 24. Consequently, the coil spring 24 causes the manufacturing cost of the ball point pen to increase. Furthermore, the front linear portion 24c of the coil spring 24 is very thin in diameter, and therefore often trapped in one of the radial grooves 3 of the ink channel member 4; which makes it impossible for the coil spring to properly urge the writing ball 21 forward.